Such a circuit arrangement is known. A brief explanation will be given in order to illustrate the problem on which the invention is based: The present invention is concerned with the end-of-life problem of lamps having two filament electrodes. Owing to an inhomogeneous material loss of the two filaments, at some point in time the emission capability of one filament compared with that of the other filament decreases. This results in the so-called cathode drop, and the resistance of a filament and thus the voltage across this filament increase compared with the corresponding variables for the other filament. This corresponds in terms of effect to the introduction of a rectification effect. This rectification effect leads on the one hand to an undesirably high load on the drive circuit, which is often in the form of an electronic ballast, and on the other hand leads to heat generation which is restricted to a very small area. In particular in the case of narrow fluorescent tubes, a heat concentration may occur which may lead to melting or breaking of the lamp. In order to establish this rectification effect, it is known to evaluate the ratio of positive and negative peaks of the lamp voltage in a protective circuit. A typical protective circuit comprises, as an essential element, an ASIC from Infineon having the designation ICB1LB01G. If it is established in the module that the ratio exceeds a predeterminable threshold value, operation of the lamp is ended.
The disadvantage of this known circuit arrangement consists in the fact that the threshold value is fixed and nevertheless filament and lamp breakages occur when using this module with different lamp types.